The ST should not have a heavy throttle.
1. Check the bar end weight is not rubbing on the end of the rubber grip; trim the grip or add a spacer washer if you need to create clearance.
2. Remove the throttle tube and clean and lube the handlebar before reassembly. Remove the bar end weight, undo the clamping screws on the throttle housing, slacken the cables at the adjuster and then slip the throttle tube off the bar. Note there is a locating peg in the lower switch pod assembly that engages with a drilled hole in underside of the handlebar. Clean the handlebar/inside of the tube of any surface rust/dirt, apply a lithium grease and reassemble.
3. Consider lubing the cables if you must, but I believe they have a teflon inner sleeve so this probably won't be needed.